Conventionally, to heat a ring-shaped workpiece, the workpiece is supported by a supporting device, e.g., a chuck mechanism, and is heated by a heating coil while being rotated. To heat a large ring-shaped workpiece, there has been proposed a heat treatment apparatus which heats the workpiece without clamping the workpiece with a chuck mechanism.
According to a first related art, a high-frequency heat treatment apparatus is configured to heat a large ring-shaped member, such as a bearing ring. The ring-shaped member is supported on a turntable, and a plurality of horseshoe-shaped heating coils are arranged in a circumferential direction of the ring-shaped member. The ring-shaped member is heated by the heating coils while being rotated together with the turntable. See, e.g., JP 2005-325409 A.
According to a second related art, a heat treatment apparatus is configured to heat the entire annular member by a high-frequency heat treatment. In this heat treatment apparatus, a large annular member is supported on a plurality of support rollers, and a radially outer surface or a radially inner surface of the annular member is pressed by three or more positioning rollers to position the annular member. The annular member is induction-heated by heating coils while being rotated. See, e.g., JP 2009-287074 A.
In the related art heat treatment apparatuses, however, the workpiece is carried in using a support tool for carrying in, and the workpiece is supported and positioned on a jig such as the turntable or the support roller when heating the workpiece, and thereafter, the workpiece is carried out using a support tool for carrying out. Thus, the workpiece is placed on different jigs or support tools when carrying in, heating and carrying out. In the case of a large workpiece, the gravity center of the workpiece has to be adjusted to stably convey the workpiece when carrying in or out the workpiece, and the workpiece has to be positioned with good accuracy when heating to realize a desired heating. For example, during the heating, a ring-shaped workpiece is rotated about a center axis thereof. Therefore, onerous work is necessary to position the workpiece, and the positioning structure is complex. Further, structures for supporting the workpiece for conveying and heating are respectively provided, so that the configuration is complex.
According to the first related art, the ring-shaped workpiece is supported and rotated on the turntable, and the workpiece needs to have a shape that fits the turntable so that the workpiece can be rotated together with the turntable. Thus, a workpiece that can be heated by the heat treatment apparatus is limited. In other words, the turntable has to be able to turn with the workpiece fixed thereto, and a turntable needs to match the workpiece to be heat treated. Thus, there is a lack in versatility.
According to the second related art, the workpiece is placed on the rotating rollers to rotate the workpiece by the rotating rollers. Thus, when the workpiece is large, so that deformation of the workpiece due to the heating is relatively large, it is not easy to maintain a constant gap between the heating coil and the workpiece. Further, when the workpiece is positioned by pressing the inner or outer surface of the workpiece by the positioning rollers, stress is applied to the heated and softened workpiece, which may result in deformation of the workpiece.